[StargazerWoods]

Don't take this as gospel, but I believe it happens when a new something or other needs to be loaded up. I have a mission I'm making at the moment that runs just fine, except I get a massive freeze very similar to what you describe right around the time a flight of aircraft are required to spawn somewhere else on the map.

I presume a ninja hardware setup will reduce this effect but of course thats not much help to those of us who can't upgrade every month/year/decade/other-time-interval.

Rob.